Regulation of Matrix Metalloproteinases by Substrate Adherence. Matrix metalloproteinases (MMPs) play a major role in many disease processes including metastasis of malignant cells and degenerative joint disorders. Recently a relationship of "dynamic reciprocity" between the extracellular environment and the regulation of a family of genes directly involved with the turnover of the extracellular matrix have been demonstrated by several investigators. Accordingly, an alteration in the extracellular matrix surrounding a given cell could lead to changes in the level of gene expression. To test this hypothesis, multiple cell lines including MG-63 human osteosarcoma cells were exposed to adherent (plastic culture plates) and non-adherent (agarose treated culture plates) conditions. PCR primer sets for human MMPs 1,2,3,7,8,9,10 and TIMPs 1,2 were utilized in RT-PCR assays to determine relative changes in mRNA levels. MMPs 1,3 and 10 mRNA levels in MG-63 cells were significantly increased (relative to aldolase) in non-adherent cells. MMPs-1,3 and 10 exhibited a 9.5 (p=0.04), 4.8 (p=0.04 and 7.0 (p=0.004) fold increase respectively in mRNA levels when exposed to non-adherent conditions for 12 hrs. MMP2 and TIMPs 1 and 2 mRNA levels were not significantly affected by the non-adherent conditions. These results would predict that extracellular changes that lead to loss of cell attachment (i.e., metastasis, trauma, and inflammation) may lead to an increase in extracellular matrix degradation by matrix metalloproteinases.